Tectonic evolution of the Sibumasu-Indochina terrane collision zone in Thailand and Malaysia: constraints from new U-Pb zircon chronology of SE Asian tin granitoids

Three principal granite provinces are defined across SE Asia, as follows. (1) The Western Thailand-Myanmar/Burma province consists of hornblende-biotite I-type granodiorite-granites and felsic biotite-K-feldspar (+/- garnet +/- tourmaline) granites associated with abundant tin mineralization in greisen-type veins. New ion microprobe U-Pb dating results from Phuket Island show zircon core ages of 212 +/- 2 and 214 +/- 2 Ma and a thermal overprint with rims of 81.2 +/- 1.2 and 85-75 Ma. (2) The North Thailand-West Malaya Main Range province has mainly S-type biotite granites and abundant tin mineralization resulting from crustal thickening following collision of the Sibumasu plate with Indochina during the Mid-Triassic. Biotite granites around Kuala Lumpur contain extremely U-rich zircons (up to 38000 ppm) that yield ages of 215 +/- 7 and 210 +/- 7 Ma. (3) The East Malaya province consists of dominantly Permian-Triassic I-type horn-blende-biotite granites but with subordinate S-type plutons and A-type syenite-gabbros. Biotite-K-feldspar granites from Tioman Island off the east coast of Malaysia also yield a zircon age of 80 +/- 1 Ma, showing Cretaceous magmatism in common with province 1. Geological and U-Pb geochronological data suggest that two east-dipping (in present-day coordinates) subduction zones are required during the Triassic, one along the Bentong-Raub Palaeo-Tethyan suture, and the other west of the Phuket-Burma province 1 belt.